In rail road freight cars in North America, the weight of the car body is borne along the tracks by rail road car trucks. The load path by which the vertical load of the car body is passed into the truck is through the body center plate. The body center plate is mounted to the rail road car body, and a mating center plate bowl is defined on the truck bolster.
The center plate bowl has the shape, in general, of a bowl. The periphery of the bowl is defined by a centrally positioned circular steel ring that stands upwardly from the upper flange of the truck bolster. It forms a cup, or hollow, inside and is sometimes provided with a liner, which may be made of a high density polymer.
The body center plate has the form of a large, downwardly protruding circular boss that seats in the bowl, on top of the liner if a liner is provided. The weight of the car is passed through the body center plate boss and into the top flange of the truck bolster. The nested relationship of the body center plate boss and the peripheral steel ring of the center plate bowl is such that the truck bolster, and hence the truck more generally, can pivot about the vertical axis of the center plate boss, thus allowing the rail car to pass over curved track.
Both the body center plate and the center plate bowl have circular central apertures that align and admit a king pin. The king pin seats in the center of the truck bolster, and the boss is located on the pin, the king pin acting as a pivot pin, or hinge pin, about whose axis the pivoting motion of the truck bolster occurs relative to the car body. In some instances, although the pin is free to rotate about its vertical axis, the pin is locked in place vertically, such that if the rail car derails, the truck may be prevented from escaping from the rail car body.
Using FIG. 1b as a guide and recognizing that FIG. 1b is not prior art, but rather an illustration provided by the present inventor for the purpose of explaining nomenclature, rail road freight cars A20 most typically have either a straight-through center sill running the full length of the car from end to end, (as may be typical in a flat car, a spine car, or a center beam car, for example) or stub center sills at either end of the car (as in gondola cars or flow-through cars such as hopper cars, pellet cars, grain cars, and so on). In each case the center sill A22 has a top flange A24 and a pair of parallel, spaced apart, downwardly extending webs A26, A28, and may have a bottom flange A30, such that a boxed hollow section is formed. In a relatively common style of center sill, a pair of Z-sections were welded together to form a hat section, with the top of the hat forming the top flange of the center sill, and the lower legs of the Z-sections forming a pair of bottom flanges on the opposed vertical webs of the center sill. Draft pockets are defined at the ends of the center sill. Draft gear and couplers are mounted in the draft pockets. Most typically, the height of the center sill tends very strongly to be a function of the allowable height of the center of the coupler, that maximum height being 34½ inches above top of rail (TOR). Since the end portions of the center sills are made to fit standard AAR coupler sizes, the center sill width between the downwardly extending flanges is generally 12⅞″ (+⅛″/−0″). The depth of the center sill is similarly generally such as to admit a coupler having a height above the coupler center line of 6{fraction (11/32)}(+/−) inches and a height below the coupler centerline of about 6⅛(+/−) inches to the outer face of the bottom flanges where the bottom flange cover plate of the draft pocket is bolted in place to retain the draft gear. Illustrations of these elements are shown at pages 652 and 653 of the 1997 Car & Locomotive Cyclopedia.
The central circular boss A36 of the body center plate A32 is usually mounted to the center sill of a rail road car at the longitudinal station of the body bolster. The body bolster, sometimes referred to as the main bolster A34, is the main laterally extending structural member of the underframe of the railroad car. Body bolsters carry vertical loads from the side sills into the center sill. Most typically, the main bolster intersects the center sill at the longitudinal station of the truck center, such that the main vertical load is passed into the center sill directly above the point of vertical reaction, namely the center plate bowl A38 on the truck bolster A40. The main bolster typically has the form of an irregularly shaped hollow cantilever beam of generally deep section at the center sill, and shallower section at the side sills. The main bolster typically has a top flange A42 that is coincident with the deck (in a flat car) or shear plate (in a grain, hopper, or pellet car), and a kinked bottom flange A44 that has a relatively deep laterally inboard portion, to which a side bearing is mounted, and a shallow outboard portion, the diminution of section being intended to clear the sideframes of the truck A46. The respective bottom flanges A44 of the left and right hand arms of the main bolster A34 most typically abut the outboard edge of the bottom flange of the center sill, such that compressive loads in the bottom flange of the main bolster are passed into the bottom flange of the center sill. A pair of spaced apart, parallel vertical webs extend between the top and bottom flanges of the main bolster, and carry vertical shear from the side sills and deck into the center sill. These webs are spaced 12 inches apart.
It is desirable to have web continuity between the webs of the left hand arm of the main bolster, and the webs of the right hand arm. This may be done, as described in the present invention herein, by providing separator plates in the nature of internal gussets, or webs, inside the main sill. It is advantageous to align those webs with the bolster webs.
In some instances, the center sill has a center sill cover plate, or bottom bolster tie plate A50, that extends between the webs of the center sill. The tie plate may have flanges, or tabs, that protrude laterally beyond the webs of the center sill. These tabs, or flanges, may be bent upwardly to give slope continuity with the bottom flanges of the left and right hand arms of the main bolster, which they meet in mating abutment.
There are at least two ways of mounting the boss of the body center plate to the rail road car body. In a generally somewhat older style of installation, the center plate assembly included a generally square, or rectangular, base plate A32 and the circular boss A36. The base plate had four corner flanges by which it was bolted to the outboard bottom flanges A30 of the center sill A22. In this style of car, a collar in the nature of a round central tube A62 was mounted inside the center sill A22 to accommodate the king pin A64, the central tube being supported in place by 4 gussets A66 on 90 degree centers: two extending along the longitudinal centerline of the car to terminate at internal separator plates inside the center sill; and two extending laterally in the direction of the main bolster centerline to meet with the webs of the center sill. This assembly was referred to as a built-in center filler. The center filler also included a bottom plate, namely tie plate A50 to which the collar and the four upstanding gusset plates were welded. The bottom plate was installed inside the center sill, flush with the bottom flanges of the center sill. This style of construction may tend to be relatively expensive to fabricate, and may be prone to cracking at the bolts and at the gussets.
Increasing car weight, and dissatisfaction with the above described style of center plate may have been factors leading to the development, in about 1975, of a different style of center plate, in the form of a center plate casting rather than a fabricated center filler assembly. In this type of casting, the collar for the king pin is integrally cast with the bearing portion of the center plate assembly. An example of this style of center plate casting is illustrated in U.S. Pat. No. 4,744,308 of Long et al., issued May 17, 1988. In this style of center plate casting, there is a boss, being the actual center plate bearing portion, and a center filler portion. The center filler portion includes a square, upstanding peripheral wall, and four integrally cast webs that join the peripheral wall to the collar and bearing portion. The peripheral wall is tapered to fit inside the four sided opening defined between the internal cross-gussets, namely the center sill web separators, and the webs of the center sill. At the base of the external, tapered face of the wall is a generally four sided shoulder. The vertices of the four sided shoulder meet at outwardly protruding lugs that have upwardly facing pads. The bottom flange of the center sill has a big, four sided hole to accommodate the center plate center filler. When the center plate casting is installed, the center filler is inserted in the big four sided hole, and the pads abut the underside of the center sill beneath the vertical webs. The center plate casting is then welded in place along the filler sides.
The present inventor has made a number of observations concerning this newer style of center plate casting. First, by being more or less square, the casting may require that the internal web separators of the center sill be spaced to give an inside clearance between them of 12⅞ inches (+⅛″/−0″). This means that the cross-gussets (i.e., the center sill web separators) may tend not to be aligned with the webs of the main bolster that are 12″ apart. In the view of the present inventor, it would be advantageous to employ a center plate assembly that would permit the cross-gussets to provide directly aligned web continuity for the webs of the main bolster through the center sill.
Second, by being more-or-less square, it may be possible to insert the center plate assembly incorrectly such that the relieved side margins of the bearing portion of the center-plate are oriented front-to-back along the center sill, instead of side-to-side. In the view of the present inventor, it would be advantageous to employ a center plate casting that is keyed to prevent mis-orientation of the casting upon installation.
Third, the four corner lugs may tend to extend radially outward from the king pin axis a distance greater than the outer wall radius of the center plate boss and a distance greater then the inner wall radius of the center plate bowl of the truck bolster. As such they may tend to overhang the peripheral wall of the center plate bowl. Since they overhang the ring, the bottom flange of the center sill must be carried higher than it might otherwise be, by a height increment corresponding to the thickness of the lug. This in turn may tend to raise the coupler centerline height, possibly undesirably far. In the view of the present inventor it would be advantageous to employ a center plate casting that is free of elements, such as the above noted lugs, that overhang the peripheral ring of the center plate bowl.
Fourth, the upwardly protruding portion of the integrally cast center plate filler has a taper, first to facilitate molding, second to facilitate installation in the generally square hole in the bottom plate of the center sill. However, given that the tolerance on the center sill must be+x/−0, (because otherwise the hole may be too small for the casting) and that the tolerance on the casting must be+0/−x, (because otherwise the casting may be too big for the hole) there is a tendency for the upwardly extending tapered wall of the cast center filler not to seat tightly against the webs and gussets of the center sill. That is to say, when the tolerances on both parts have to be to opposite sides of the desired dimension, there will be a tendency for the tolerance build up to result in a gap between the parts. Consequently, when the casting is welded along the reliefs of the rectangular shoulder, there is a tendency for the weld to blow through the gap. This may be highly undesirable from a manufacturing viewpoint. Further still, the square design with the lugs may tend to require a stop-and-start style of welding along four chamfered reliefs. The present inventor has observed that this style of welding may tend to result in poor welds more often than perhaps might otherwise be the case. In the view of the present inventor, it may be advantageous to employ a continuous circumferential weld, rather than the stop-and-start style.
Fifth, the integral center plate casting necessitates the existence of a big, relatively sharp-cornered square hole in the bottom flange of the center sill, directly opposite the juncture of the bottom flanges of the main bolster with the center sill bottom flange. This large square hole may have tended to weaken the center filler area of the car, by removing the center sill bottom cover plate in the area, and it may tend to interrupt, or interfere with load transfer in the surrounding structure. It would be advantageous not to require this large, badly shaped (i.e, with squared, fairly sharp corners) hole, but rather to employ a plate to provide a large measure of flange continuity across the center sill.
Sixth, the presently used plug type center plates require a relatively significant amount of surface preparation adjacent to the opening in the center sill. It would be advantageous to employ a center plate that requires less work to prepare.